System for sound reproducing apparatus



Patented Mar. 8 1938 Robert H. Dreisbach, Fort Wayne, Ind., assignor toElective-Acoustic Products Company, Fort Wayne, Ind., a. corporationrofIllinois Application .iune 6, 1936, Serial No. 83,950

6 Claims.

The present invention relates to a system for sound reproducingapparatus, and more particularly to anaddress and program reproducingsystem for schools and like institutions.

5 An object of the invention is to provide in a sound reproducing systemhaving a plurality of sound reproducing devices, switching means wherebyany number or all of said sound reproducing devices may be selectivelyswitched into and out of the system without affecting the volume ofsound reproduced by the operating devices.

Another object of the invention is to provide a novel form of switchingmeans in a system of the above character whereby the full poweravailable may be directed to a particular group of' '25 soundreproducing devices may be connected to the system at any timeirrespective of the positions of-the independent "speaker controllingswitches and without disturbing the volume of sound reproduced by saidsound reproducing devices.

Other objects and advantages of the invention will be in part pointedout and in part evident to those skilled in the art, from the followingdescription taken in connection with the accompanying drawings, whereinthere is shown, by way of illustration and not of limitation, apreferred embodiment of a system designed primarily for school purposes.

In the drawings- I I Figure 1 is a schematic one line diagram showing acomplete distribution system,

' Figure 2 is a perspective view of a preferred form of desk typedistribution panel, and

Figure 3 is a partial wiring diagram showing 45 a switching systemembodying the present invention, which is suitable for a high school ora college.

For the purpose of illustrating the invention, the applicant has shown,by way of illustration, a sound transmission system for schools ln-which"classroom is provided with one or more speakers and auxiliary soundreproducing devices are located at various other locations, as in anauditorium, atthe athletic field and in the gym- 55 nasium or othermeeting halls.

As illustrated in Figure 1 of the drawings, the complete system providesfor spoken programs, phonographic'reproductions and radio programs.These programs are adapted to be connected through suitable? mixers andamplifiers to. a 5 distribution panel where the selected program may bedistributed throughout the system as desired.

More specifically, the system, as illustrated in Figure 1, will comprisesuitable input and power amplifiers I0 and ii, into which the pickup ofa desk microphone l2, or a pedestal microphone l3, may be selectivelyintroduced through a-mixer i 4. A second mixer 15 will also be providedthrough which the output of a phonograph reproducer l6 or a pedestalmicrophone, connected to a receptacle l1, may be introduced into theamplifiers l0 and II. A third mixer l8 provides for the introduction ofthe output of a radio receiver l9, into the amplifiers It! and H.Connected to the mixer l8 there is also an auxiliary inlet receptacle2ll,'to which a pedestal mircrophone or other source of modulatedcurrent may be connected. The output circuit of the amplifiers l0 and His connected with a distribution panel 2|, which will be described indetail hereinafter. Connected to the distribution panel 2|, as willhereinafter appear, are a plurality of groups of speakers 22, 23, 24 and25, which are respectively located in the auditorium, at the athleticfield, in the gymnasium and in the individual room of the schoolbuilding. Associated with the power amplifier, there is also provided asuitable monitor speaker 26 and a volume indicating instrument 21.Suitable switches 28, 29 and 30, for connecting the various mixerstotheir associated source of modulated current may also be provided,together with means 3| for controlling the output volumetherefrom.

As illustrated in Figure 2 of the drawings, the preferred form ofcontrol cabinet incloses, all of the necessary apparatus for thecomplete switching operations necessary between the micro phone,phonograph or radio and the various sound reproducing devices. In itspreferred form, the distribution panel 2| is mounted centrally upon acabinet 32 with a radio receiver 33 at one side and a mixer and volumecontrol panel 34 at the other side. In this figure of the drawings, thedistribution panel 2| is shown as '50 having apl'urality of independentroom switches and the various other switches of the circuit disposedtherebelow. The radio receiver 33 is preferably of the all-wave type,having a tuning dial 7 35 and various control knobs 36. Themixer con- I1 across the output circuit 01' the amplifier l6 and trol panel 34 atthe right of the distribution panel 21 carries the volume indicator 21,the switches 28,26 and 30 and the mixer controls l4, I5 and I8, showninFigure 1 of the drawings. A suitable switch 31 is also shown forconnecting the volume indicator 2'! in the circuit of the particularsource of modulated current selected by the mixer controls l4, l5-or i8.

The distribution panel 2| carries a suitable power switch, designated bythe numeral 40, for

connecting the complete system to the service lines of the schoolbuilding. This switch is preferably disposed upon the lower part of thepanel 2|, and adjacent thereto, upon opposite sides, is a microphoneplug receptacle 4| and a phonograph plug receptacle 42, for the attach-I ment respectively of a desk microphone and a local phonograph unit. Inconnection with the latter plug receptacle, it should be stated that insome instances the phonographic reproducer may be built into the cabinet32. The desk microphone may also be permanently connected to theapparatus if desired. The panel 2| also carries a monitorspeaker switch43, a master room switch 44, a full power switch and a plurality ofindividual speaker switches 46.

In the drawings, the panel 2| is equipped with forty-two (42) switches46, which are adapted to individually control as many sound reproducingdevices. If the apparatus is to be used I with a fewer number 01' soundreproducing devices, the switches 46, not in use, may be omittedaltogether, 'or merely disregarded insofar as connections are concerned,as desired.

One of the novel features of the present inment of the volume controlsor effecting the sound I6 is connected and, disconnected from theswitching system. The main switch 56 is of the single pole'double throwtype. Connected across the-conductors 41 and 46, between the amplifierl6 and the main switch 56, by means of conductors 5| and 52, is themonitor speaker 26 and the volume indicator 21. Arranged adjacent andconnected between one of the poles of the main switch 66 and theconductor 46, there is a dummy load or impedance 66. With thisarrangement it 'wiiibe seen that when the main switch 66 is moved-intoits panel disconnecting position it will connect the dummy load orimpedance 66 permit an adjustment at the panel 01' the tonal volume ofthe amplifier output with the monitor speaker'before any of the otherspeakers are put in operation. Under these conditions the impedance 66will serve to load the amplifier with an impedance corresponding to thetotal impedance of the circuit when all of the speakers itor speaker, itwill then be possible to connect the system to .the amplifier output andoperate such speakers as are connected with the system at a propervolume.

In order to permit the full power of the amplifier to be directed to anyspecial location, as for example, to a large auditorium, the athleticfield or other location, the conductor 41 is connected to one blade ofthe full power switch 45, and the other blade of this switch isconnected to a conductor 54 which furnishes power to the soundreproducing devices at the location selected. The other side of thesound reproducing devices, designated by the numeral 22, are thenconnected to the other side of the amplifier l0 through the conductors55 and 48. The full power switch 45, when in its on or up position, willserve to connect a suitable power converting transformer 56 into thecircuit formed by the conductors 41 and 54, which connects the selectedgroup of speakers with the amplifier l0.

In the example chosen for illustration in this figure of the drawings,there is shown only one full power switch 45 for controlling the powerof the auditorium speaker or speakers 22. Where additional locations aredesired, as for example in a cafeteria, at the athletic field, or othermeeting hall, and full power is desired, additional switches similar toand,conn'ected as is the switch 45, will be provided. In connection withsuch additional switches there may also be provided additional impedancecohverting transformers 56, having 'the required i'mpedance convertingcapacities.

In order not to complicate the switching di- 'agram now underconsideration, the sound reproducing devices or loud speakers 22, 25 and26 are shown as of the permanent magnet type, and consequently only theconductors which form the modulated voice or other sound currents areshown. Where loud speakers of the electrodynamic type, involving anenergized field, are used, it is to be understood the fields thereofwill be excited in-the usual manner by separate conductors.

- Inthe drawings, the master room switch 44 is shown as located at thetop of a vertical row of horizontally disposed switches 46. The adjacentone of these switches is connected to control the auditorium speaker 22in a manner similar to that contemplated for the control of theindividualroom switches. Extending downwardly adjacent the vertical rowof horizontally disposed switches 46, there is provided (our (4) busbars or conductors 61, 56, 66 and 66. As here shown, the switches 46 areall of the double pole double throw type, and as connected they' .willbe, as indicated, in their on' or. F'speaker circuit closing positionwhen left, and in their "oil!" or speaker circuit opening position whenthrown to the right. Withjthis arrangement it will be seen that when themaster roomswitch 44 is in its "01! position and the full powerauditorium switch 46 is in its down or' a circuit will be established-.through a conductor 6|, .the uppenblade of the off position,

master room switch 44, through'a conductor or any-of the room switches46 are in their "oil!" '62, tothe bus bar 51. Now, if the auditorium,

position, a circuit will be established from the bus bar 61, throughconductors 66 leading there,-

from to the corresponding speaker switch 46,-

through the lower blade "of said speaker switch, and by way ofconductors 64 to associated dummy load impedances 66, and back throughthe bus switch 44, and back to the conductor 48 at the other side'of theamplifier output. If any one of the speaker switches 46 is now thrown tothe left or into its "on or speaker energizing position, the dummy loadimpedance 65 associated therewith will be cut out of the circuit and anew connection will be established to the particular speaker from, theamplifier output conductor 41 through the left-hand blade of the fullpower auditorium switch 45, a portion of the conductor 6|, and throughthe conductor 66 to the bus bar 59, from whence the current will flowthrough the upper blade of the particular on room switch, via anassociated conductor 61, to the particular speaker 25, and to ground, asindicated at the points 68, and by virtue oi the ground 49 at thesource, complete a circuit back to the conductor 48 at the other side ofthe rooms and/or locations provided for by the sysamplifier l0.

At this point it should be stated that the dummy load impedances 65,associated with the.

several room switches 46, of which there will be a number correspondingto the number of term, each have an impedance value corresponding to theimpedance of .thexparticular speaker which it is to be substituted forwhen the particular speaker is disconnected from the system.

Now, if the master room switch 44 is thrown to the left or to its onposition, the current flowing from the conductor 41 will pass throughconductor 61, as described above, and by virtue of the jumper conductor69 connected in the master room switch 44, and the conductor 10, bedistributed between the buses 58 and 60, so that those room switcheswhich are in their on position will complete, the speaker circuits, asindicated above, and those speakers having their associated switches inthe off" position 40 will be completed from the bus bar 50 through theupper blades of the switches 46 and back to the amplifier 10, throughthe conductors 61 and the ground connection, as previously suggested.Under these conditions, with less than all of the room speaker controlswitches 46 in their on position, should the master room switch be thenthrown back to its off" position, circuits will then again bereestablished through the dummy load impedances 65, and thus the totalimpedance of the system will be maintained constant, and as a result,the sound reproduced by the remaining connected speakers will remain atthe same volume without requiring any adjustment of the volume controlmeans.

As shown in the diagram of Figure 3, the audi-" torium speaker 22 alsohas a switch 45 upon the panel 2|, by means of which it may be throwninto the circuit or cut outoi! the circuit, as desired, when the roomspeakers 25 are in operation. In connection with this use it is possiblethat a plurality oi! speakers 22 may be used where the size of theauditorium warrants, and in such an event the dummy load or impedance 65associated therewith will be of a difl'erent impedance value than theimpedance units associated with the individual loudspeakers 25. In thisdiagram only four .(4) room speakers 25 have been illustrated. However,it is understood that this number may be multiplied to any extentdepending upon the capacity 01' the amplifier ill to supply currenttherefor. The additional room speakers will, of course, be connected ina manner similar to, that illustrated with the four (4) room speakersshown in the drawings. When the auditorium speaker 22 is operated withless than full power, as when the full power switch 45 is in its oil? ordown position, the circuit of this loud speaker will be completed fromthe conductor 41 throughthe adjacent pole of the full power switch 45,-the conductor 66, through the upper blade of the auditorium switch 46and back to the right-hand blade of the full power switch 45, throughtheconductor 69, and then by way of conductor 54. to the speaker 22, andthrough conductor 55 to the conductor 48, at the other side of theamplifier l0.

Upon further inspection of the above described circuit, it will be seenthat the bus bar or conductor 51 will be energized only when the masterroom switch 44 is in its ofi or normal position, and that the bus bars58 and 60 will be energized only when the master room switch 44' is inits on" position. This, therefore, means that the bus bar 59, which asdescribed above is connected with the amplifier output conductor 41,provides a circuit from the amplifier l0, through the ground connections68, for each of the individual speakers 25; whenever a correspondingroom switch is thrown into, its on position, irrespective of theposition of the master room switch 44.

From the above, it will be seen that there is provided by the system ofconnections described,

an arrangement wherein any one or a number less quiring any adjustmentof the volume controlling means at the. source of the speaker operatingmodulated current. The arrangement also provides for a segregation ofthe total output of the source of modulated current to any particulargroup of speakers independently of the remaining speakers of the system,and by the provision of the dummy load impedance 53, in connection withthe main switch 50, the described system also provides a means wherebythe sound reproducing volume of the speakers in the system may beproperly adjusted by reference to a monitor speaker and/or indicatingmeter, independently of the sound reproducing devices or speakers whichmay be later connected to the system.

While Ihave, for the sake of clearness and in order to disclose myinvention so that the same can be readily understood, described andillustrated specific arrangements, I desire to have it understood thatthis invention is not limited to the specific arrangements'disclosed,but may be embodied in other ways that -will suggest themselves topersons skilled in the art. It is believed that this inventidn is newand it is desired to claim it so that all such changes as come withinthe scope oi the appended claims are to be considered as part'oi thisinvention.

Having thus described myinvention, what I claim and desire to secure byLetters Patent is 1. In an address system for public buildings, thecombination of a source of modulated current, a plurality of loudspeakers adapted to be operated by, said modulated current, switchingmeans associated with each of said loud speakers having open and closedcircuit positions for independently connecting and disconnecting samewith respect to said source of modulated current, and a master switchfor connecting all of said loud speakers to said source of modulatedcurrent irrespective of the positions of the switching means associatedwith each of saidloud speakers.

2. In an address system for public buildings,

the combination of a source of modulated current, 75 v a plurality ofloud speakers adapted to be operated by said modulated current,switchingmeans associated with each of said loud speakers for connectingand disconnecting sameto said source of modulated current, a loadresistance associated with each of said loud speakers having animpedance corresponding to that of the loud speaker, switching means foralternately connecting a speaker or a load'resistance to said source ofmodulated current, and a master switch for disconnecting saidload'resistances and connecting all of said loud speakers to said sourceof modulated current independently 01 their respective switching means.

3. In an address system for public buildings, the combination of asource of modulated current, a plurality of loud speakers adapted to beoperated by said modulated current, switching means associated with eachof said loud speakers for connecting and disconnecting same to saidsource of modulated current, a plurality 01' load resistance unitshaving an impedance correspondingto that of each speaker and adapted tobe substituted one at a time in the modulated current circuit when aspeaker is disconnected therefrom, and a master switch for disconnectingall 01' said resistance units and connecting all of said loud speakersto said source oi modulated current independently of their respectiveswitching means.

4. In a constant impedance sound reproducing system of the characterdescribed, the combinameans for connecting and-disconnecting saidimpedance changing transformers without aflecting the controlestablished by said first switching means.

5. In an address system for public buildings, the combination of asourceof modulated current, an amplifier for controlling the value ofsaid modulated current, a plurality of loud speakers and impedancesadapted to be optionally connected to said amplifier, switch means forcontrolling the optional operation of said loud speakers and/ orimpedances, a monitoring loud speaker adjacent said source of modulatedcurrent for observing the tonal volume produced by said amplifier, aresistance unit having an impedance corresponding to the total impedanceof the optionally chosen loud speakers and impedances connected to saidamplifier, and a second switching means for disconnecting all of saidloud speakers and impedances from said amplifier and connecting saidresistance unit into said circuit, whereby said modulated current sourceand said amplifier will operate under an artificial load conditioncorresponding to the total load impedance thereupon when said chosenloud speakers and/or impedances are connected to said source ofmodulated current.

6. In a systemof the character described, the combination of a source oimodulated current, an amplifier connected to said source of modulatedcurrent having a plurality of sound reproducing devices connectedthereto, means for controlling the output volume of said amplifier, amonitor speaker for observing the volume control effected by said volumecontrol means, a microphone adapted to be connected into said amplifiercircuit for transmitting announcements through said sound reproducingdevices, and switching means for simultaneously disconnecting saidmonitor speaker when said microphone is connected into said amplifiercircuit to prevent a feed-back from the monitor speaker into saidmicrophone.

ROBERT H. DREISBACH.

